This invention relates to certain amorphous perfluoropolymers which are particularly suitable as cladding materials in optical fiber constructions.
Various fluoropolymers have been proposed from time to time for this purpose, mainly because of their good performance under a variety of temperature and atmospheric conditions and resistance to many chemicals. A good polymeric cladding material for optical fibers should be completely amorphous because crystallites present in polymers would cause light scattering. Further, it should have a high glass transition temperature, Tg, especially if intended for use at high temperatures because above its Tg it would lose some of its desirable physical properties and in particular it would be unable to maintain good bonding to the fiber core. A desirable Tg would be above 85.degree. C., preferably above 120.degree. C. Entirely amorphous fluoropolymers having significantly high Tg's have not been heretofore reported.
U.S. Pat. No. 3,978,030 to Resnick describes certain polymers of perfluoro-2,2-dimethyl-1,3-dioxole (PDD), which has the following formula: ##STR1## The above patent describes both homopolymers of PDD, which are not further characterized, and acrystalline copolymer with tetrafluoroethylene (TFE), which has a melting point of about 265.degree. C.